Bidirectional texture functions, or BTFs, model reflectance variation at a meso-scale as a function of lighting and viewing direction. BTF is a 6D function of position p on the reference plane, view direction v, and lighting direction l that records the resulting radiance at p viewed in direction v and lit in direction l. BTFs capture view-dependent visibility variation, also called masking or parallax, but only within surface contours. Mesostructure detail is neglected at silhouettes, so BTF-mapped objects retain the coarse shape of the underlying model.